A single shot hit the Iraqi in the chest and killed him instantly. It had been fired from a range of 1,250 meters, well beyond the capacity of the powerful Leupold sight, accurate to 1,000 meters.

"I believe it is the longest confirmed kill in Iraq with a 7.62mm rifle," said Staff Sgt Gilliland, 28, who hunted squirrels in Double Springs, Alabama from the age of five before progressing to deer - and then people.

"He was visible only from the waist up. It was a one in a million shot. I could probably shoot a whole box of ammunition and never hit him again."

Later that day, Staff Sgt Gilliland found out that the dead soldier was Staff Sgt Jason Benford, 30, a good friend.

The insurgent was one of between 55 and 65 he estimates that he has shot dead in less than five months, putting him within striking distance of sniper legends such as Carlos Hathcock, who recorded 93 confirmed kills in Vietnam. One of his men, Specialist Aaron Arnold, 22, of Medway, Ohio, has chalked up a similar tally.

"It was elating, but only afterwards," said Staff Sgt Gilliland, recalling the September 27 shot. "At the time, there was no high-fiving. You've got troops under fire, taking casualties and you're not thinking about anything other than finding a target and putting it down. Every shot is for the betterment of our cause."

All told, the 10-strong Shadow sniper team, attached to Task Force 2/69, has killed just under 200 in the same period and emerged as the US Army's secret weapon in Ramadi against the threat of the hidden Improvised Explosive Device (IED) or roadside bomb - the insurgency's deadliest tactic.

Above the spot from which Staff Sgt Gilliland took his record shot, in a room at the top of a bombed-out observation post which is code-named Hotel and known jokingly to soldiers as the Ramadi Inn, are daubed "Kill Them All" and "Kill Like you Mean it".

On another wall are scrawled the words of Senator John McCain: "America is great not because of what she has done for herself but because of what she has done for others."

The juxtaposition of macho slogans and noble political rhetoric encapsulates the dirty, dangerous and often callous job the sniper has to carry out as an integral part of a campaign ultimately being waged to help the Iraqi people.

With masterful understatement, Lt Col Robert Roggeman, the Task Force 2/69 commander, conceded: "The romantic in me is disappointed with the reception we've received in Ramadi," a town of 400,000 on the banks of the Euphrates where graffiti boasts, with more than a degree of accuracy: "This is the graveyard of the Americans".

"We're the outsiders, the infidels," he said. "Every time somebody goes out that main gate he might not come back. It's still a running gun battle."

Highly effective though they are, he worries about the burden his snipers have to bear. "It's a very God-like role. They have the power of life and death that, if not held in check, can run out of control. Absolute power corrupts absolutely.

"Every shot has to be measured against the Rules of Engagement [ROE], positive identification and proportionality."

Staff Sgt Gilliland explains that his Shadow team operates at the "borderlines" of the ROE, making snap judgments about whether a figure in the crosshairs is an insurgent or not.

"Hunters give their animals respect," he said, spitting out a mouthful of chewing tobacco. "If you have no respect for what you do you're not going to be very good or you're going to make a mistake. We try to give the benefit of the doubt.

"You've got to live with it. It's on your conscience. It's something you've got to carry away with you. And if you shoot somebody just walking down the street, then that's probably going to haunt you."

Although killing with a single shot carries an enormous cachet within the sniper world, their most successful engagements have involved the shooting a up to 10 members of a single IED team.

"The one-shot-one-kill thing is one of beauty but killing all the bad dudes is even more attractive," said Staff Sgt Gilliland, whose motto is "Move fast, shoot straight and leave the rest to the counselors in 10 years" and signs off his e-mails with "silent souls make.308 holes".

Whether Shadow team's work will ultimately make a difference in Iraq is open to question. No matter how many insurgents they shoot, there seems no shortage of recruits to plant bombs.

Col John Gronski, the overall United States commander in Ramadi, said there could not be a military solution. "You could spend years putting snipers out and killing IED emplacers and at the political level it would make no difference."

As they prepare to leave Iraq, however, Staff Sgt Gilliland and his men hope that they have bought a little more time for the country's politicians to fix peace and stability in their sights.